WARSAW, March 10 (Reuters) - Poland's prime minister said onMonday he would ask Chancellor Angela Merkel to work to reduceGerman and European dependence on Russian gas to avert"potential aggressive steps by Russia in the future".

Merkel will visit Poland on Wednesday to discuss the crisisin Ukraine, where Russia has effectively taken control of thesouthern Crimean peninsula. Events there have highlightedEuropean reliance on Russian oil and gas.

Ukraine is a major gas transit nation for supplies fromRussia to the European Union (EU), which relies on Russia forover a quarter of its gas.

"Germany's dependence on Russian gas may effectivelydecrease Europe's sovereignty. I have no doubts about that,"Prime Minister Donald Tusk told a news conference.

"Increasingly more expensive energy in Europe due toexorbitant climate and environmental ambitions may also meangreater dependence in Russian energy sources...Hence, I willtalk (to Merkel) primarily about how Germany is able to correctsome economic actions so that dependence on Russian gas doesn't paralyse Europe when it needs...a decisive stance."

Germany has been one of the strongest proponents ofincreasing the share of renewable energy sources in Europe.Poland gets nearly all its energy from domestically producedcoal and has opposed these efforts in the past.

"The question of Ukraine is a question of EU's future, EU'ssafety, and a correction of EU's energy policy," Tusk said.

"We will not be able to efficiently fend off potentialaggressive steps by Russia in the future, if so many Europeancountries are dependent on Russian gas deliveries or wade intosuch dependence," he added.

Poland is the largest central European economy and has playeda role in diplomatic efforts of the European Union in the worststand-off between the West and Russia since the end of the ColdWar.

Four central European countries have already asked the U.S.Congress to make it easier for them to import natural gas fromthe United States and reduce their dependence on supplies fromRussia.

Last year, Russia's gas export giant Gazprom supplied EU and Turkey with a record 162 billion cubic metres ofgas, of which 86 bcm went via Ukraine.

Gazprom issued a veiled warning last week that it could stopshipping gas to Ukraine over unpaid bills, bringing to mind abrief disruption in deliveries during a dispute between Russiaand Ukraine during a cold winter in 2009.

European Energy Commissioner Guenther Oettinger said he didnot expect Russia to switch off gas supplies to Europe over theUkraine crisis. If no more gas flowed through Ukraine, it wouldaffect 14 percent of European gas consumption, he added.